I'm also using `akka-zeromq` and would like to see the JeroMQ switch being made.
From what I now understand, it's not dual-licensed. There's a `COPYING.LESSER` + `COPYING` file since GNU says to include both for LGPLv3:

> "...since the LGPL is a set of additional permissions on top of the GPL, it's important to include both licenses so users have all the materials they need to understand their rights." (https://www.gnu.org/licenses/gpl-howto.html).

Pieter Hintjens also confirmed that it's
> "LGPLv3 with a static link exception" (http://lists.zeromq.org/pipermail/zeromq-dev/2014-June/026267.html).

Not 100% sure about the "special exception" consequences though...